The present invention relates to a gearing arrangement for driving a photosensitive drum of an electrophotography process unit.
Referring to FIG. 1 for illustrating a conventional electrophotography process unit, the surface of a photosensitive drum 28 is uniformly charged with a constant voltage by an electric charger 25 and then exposed to the light of a lamp 22 reflected from an original document placed on a platen glass 21, so that an electrostatic latent image is formed on the photosensitive drum 28 corresponding to the image of the document. The light source may be a laser scanning unit, light emitting diode, etc. Thereafter, as the photosensitive drum 28 is rotated, the toner of a developer 27 is attracted to the surface of the photosensitive drum 28 so as to develop the latent image transferred by a transfer means 32 to a sheet of paper supplied by a supply roll 20.
The paper adhering to the photosensitive drum 28 by the electrostatic force is separated by a separator 33 therefrom. Then the paper is conveyed by a conveyor belt 30 to a fixing means 40, where the paper is heated and pressed between a heat roll 35 and pressure roll 34 to fix the toner, conveyed to a discharging tray 39.
The residual toner on the photosensitive drum 28 is removed by a cleaning blade 29 and the latent image is canceled by the light supplied from a pre-erase lamp array 37.
Referring to FIGS. 3A and 3B, the rotation of the drum 28 is made by the rotational force of the drive gear 22 of a motor, which rotational force is transmitted to the drum 28 by means of a pulley 22a attached to the shaft of the drive gear 22, a pulley 44 attached to the shaft of an idle gear 43, and a timing belt 45 connecting the pulleys 22a and 44. The idle gear 43 is engaged with a first drum gear 28a mounted on one end of the shaft of the drum 28. The drive gear 22 is engaged with an idle gear 41 of different pitch. An idle gear 42 is engaged with the idle gears 41 and 43. A magnet roll drive gear 27a mounted on one end of the shaft of a magnet roll 27b is engaged with an idle gear 46 which in turn is engaged with the idle gear 43. The magnet roll 29b is installed in the developer 27.
Such conventional gearing arrangement for transmitting the torque of a servo motor to the drum and developer is very complicated requiring the timing belt. Moreover all the driving components are positioned only in one side of the drum, so that the torque is concentrated in that side of the drum to make unstable the gap between the drum and developer, thereby degrading the picture quality of document reproduction.